I took the domain for my cleric of shar and immediately noticed an issue with the "Immune to darkness" ability.
"Immune to darkness" is only half-useful.
This because Darkness spell has two effects.
First it causes a special darkness blindness to anyone in it
Secondly, and also gives a special "invisibility obscuring" effect to anyone in it.
Being "immune to darkness" means you are not blinded, but in no way does it mean that you can see creatures obscured by the darkness, so anyone entering your darkness effectively becomes invisible to you.
At the end of the day you still have to cast ultravision or you are making creatures invisible to you and then you can't target them anymore.
Trying to rely on the darkness immunity always ends up in a mess. If you are ranged, yes, you can cast darkness on yourself and shoot at the enemy that can't see you, but the AI or the PCs will walk inside the darkness and when they enter, they'll be obscured to you and you can't target anymore. If you are melee and cast darkness on the enemy to go attack them, then they'll be obscured and you'll not only have to find them first but you'll also get the 50% miss chance on them because you can't see them.
I'd suggest the "immune to darkness" ability be removed entirely and the domain be simply given a "Domain power" that is just ultravision that can only be self-cast.
Ultravision is the only true immunity to darkness that exists in NWN.